Concrete units are available in a wide range of sizes and shapes, and are used for a variety of applications ranging from concrete blocks and bricks for building construction to landscaping units, including segmental retaining wall blocks (the latter are sometimes called “SRW” blocks).
Depending on the intended end-use application of the concrete units being produced, the surface appearance of the units may be important, and the marketplace has come to expect various decorative or cosmetic surface finishes for many units. Such surface finishes include those commonly described as broken or split, striped, striated, simulated broken, and smooth (alone or in combination with one of the other surface finishes). One such surface finish is a texture that resembles the appearance of a “split” rock. A “split” surface finish on a concrete unit may be achieved by mechanically splitting away a portion of a face of the masonry unit. This is typically achieved with a mechanical splitting blade similar to a guillotine, and the splitting is performed on the units after they have been cured or hardened. To avoid waste, this is often done by first forming the units as “Siamese” twins and then splitting them apart. The resulting fracture surface on the front face of both blocks is generally thought to be aesthetically pleasing and decorative.
The mechanical splitting of units is an added cost of processing. This cost provides an incentive to develop new methods of roughening the surface of concrete units to create a desirable surface finish without the need to mechanically split the masonry units. Although some approaches have involved processing steps to be performed on the green or uncured masonry units immediately after they are discharged from the mold, one common approach has been to modify the mold in some fashion so that a roughened surface is produced on the concrete units as they are ejected from the mold (i.e. the units are roughened in the mold cavity).
At times, it is desired to produce a more modest or fine roughening of a masonry unit than is typically produced when mechanically splitting a block. Unfortunately, the molds used to produce pronounced roughening are often unsuited for the more modest roughening. If they are scaled down to produce more moderate roughening, they often have more delicate features that lack the desired strength and wearability. Modest roughening of one or more surfaces of a concrete unit such as a brick or block is useful not only as the only surface finish, but it is useful in combination with mechanical splitting where the modest roughening can be performed on surfaces of the block which are not to be mechanically split, but which may be visible to the observer when the products are used, for example, to create a retaining wall. By roughening the surfaces immediately adjacent to the mechanically split surface(s), light striking the adjacent surfaces is scattered and the reflections associated with smooth reflective surfaces are avoided.